An active matrix organic light-emitting diode (AMOLED) display has been widely used over time because it can meet the requirements of a high-resolution and large-size display device.
For an AMOLED, a thin film transistor (TFT) generates a driving current in a saturation state so as to drive an organic light-emitting element, such as an organic light-emitting diode (OLED), to emit light. The OLED has attracted much attention and thus has been widely used in the field of organic light-emitting technology due to such advantages as low power consumption, high brightness, low production cost, wide viewing angle and rapid response.
When the organic light-emitting element is driven to emit light, it is required to inject electrons and holes between a transparent electrode layer as an anode and a metal electrode layer as a cathode respectively. The electrons and holes are recombined at a light-emitting layer, so as to change the electrons from an excited state to a ground state and thereby to release the excess energy in a form of light. However, the holes and electrons are injected into the light-emitting layer from the anode and the cathode respectively, and there usually exist some excess holes or electrons that do not take part in the recombination, so the efficiency of recombination is low. In addition, when an existing pixel circuit drives the organic light-emitting element to emit light, a transmission direction of the holes or electrons remains unchanged, and the excess holes or electrons that do not take part in the recombination may be accumulated at a surface of a hole transmission layer/electron transmission layer, or may get over a potential barrier and flows into the electrodes. Along with a long-term use of the organic light-emitting element, a large number of un-recombined carriers will be accumulated at an internal interface of the light-emitting layer, so that a built-in electric field is formed inside the organic light-emitting element. As a result, a threshold voltage of the organic light-emitting element is increased continuously, the brightness is decreased continuously, the energy efficiency is reduced gradually and the aging of the organic light-emitting element is getting worse.